OK, I've only had my 9900 for three weeks and was experiencing the phantom cursor issue quite badly, where all of a sudden it would jump all over the place.
My solution.
1. Sit in van with door ajar with 9900 on lap about to send an email.
Luckily, the damage was hardly noticeable. Just a slight nick in the rear rubberized surround and the phone works just fine with no more cursor problems.
This says to me that the issue must be hardware related for a knock to fix it.
DON'T TRY THIS METHOD YOURSELF GUYS. (But it worked for me)
Yes it's the connector inside the phone that connects the keyboard/buttons and trackpad to the motherboard. Very common that it comes loose. Easy fix but invalidates warranty unless using your method.
I've lost trackpad and buttons through dropping, but never the other way around. Although I did try it a few times before relutantly opening her up. :-)
I don't have any issues with my 9900 at all but I do have a little bit of keypad wear. August 16th my one year warranty will be up. Then I'll replace it along with the bottom chin piece which was damaged from my old original otterbox defender (redesigned replacement doesn't scratch the phone). Can't wait to have it looking brand new again.